Electronic musical instrument keying assembly providing a minimum of electrical noise

ABSTRACT

A switch for an electronic organ or other electronic instrument, which produces a minimum of electrical noise even when low level electrical signals pass through the switch for later high gain amplification. The switch includes a cylindrical wire connected to a tone generator, and a strip of conductive elastic material which can be deflected against the wire and that spreads onto the wire to gradually increase the contact area therewith and decrease the contact resistance. An electrically conductive lubricant is applied to the wire and elastic strip so that as the elastic material of the strip spreads under pressure, the spreading portions smoothly slide outwardly. An insulator strip is fastened to the elastic conductive strip, and another elastic conductive strip is fastened to the insulator and is grounded, to shield the first conductive strip from stray electrical currents.

Unite States Patent Nelson, .11.

[ 1 Nov. 6, 1973 [75] Inventor: Carl S. Nelson, Jr., Los Angeles,

Calif.

[73] Assignee: Opsonar Organ Corporation, Bronx,

221 Filed: Apr. 24, 1972 21 Appl. No.: 247,056

[52] U.S. C1. 84/l.01, 84/DIG. 7, 200/159 B,

307/116, 340/365 R [51] Int. Cl. ..G10h l/00 [58] Field of Search214/101, 1.04, 1.09,

84/1.l,1,27, DIG. 7, 423, 427, 433, 439, 440; 200/159 R, 159 A, 159 B;338/69, 307/116;

3,626,350 12/1971 Suzuki et a1. 338/69 3,643,041 2/1972 Jackson 200/159B 3,657,459 4/1972 Peterson et 211.. 84/1.0l 3,668,337 6/1972 Sinclair200/159 B X 3,694,559 9/1972 Suzuki et al. 154/101 PrimaryExaminer-Richard B. Wilkinson Assistant Examiner-Stanley .1. WitkowskiAttorney-Seymour A. Scholnick [57] ABSTRACT A switch for an electronicorgan or other electronic instrument, which produces a minimum ofelectrical noise even when low level electrical signals pass through theswitch for later high gain amplification. The switch includes acylindrical wire connected to a tone generator, and a strip ofconductive elastic material which can be deflected against the wire andthat spreads onto the wire to gradually increase the contact areatherewith and decrease the contact resistance. An electricallyconductive lubricant is applied to the wire and elastic strip so that asthe elastic material of the strip spreads under pressure, the spreadingportions smoothly slide outwardly. An insulator strip is fastened to theelastic conductive strip, and another elastic conductive strip isfastened to the insulator and is grounded, to shield the firstconductive strip from stray electrical currents.

5 Claims, 10 Drawing Figures PATENTED MIN 6 I975 SHEET 10F 3 ELECTRONICMUSICAL INSTRUMENT KEYING ASSEMBLY PROVIDING A MINIMUM OF ELECTRICALNOISE BACKGROUND OF THE INVENTION This invention relates to electricalmusical instruments.

One type of electronic organ includes a series of signal sources, a highgain amplifier, and a keyboard that can be operated by a musician toselectively connect different signal sources to the amplifier. Thesignal sources, may generate only a very low level signal, so that ifthe keyboard switches generate even a low level of noise, the noise willbe greatly amplified with the musical signals and will be noticeable inthe organ output. Noises of the switch arise from several sources. Onesource of noise arises from the suddenness of electrical contact whichcan allow sudden discharges of currents and the creation of poppingsounds. This can be minimized by utilizing an elastic resistive con tactmember for gradually establishing contact. However, the contact areamust increase very rapidly with slight increases in displacement of theoperating key if the contact resistance is to quickly fall to a lowlevel. Where a pair of flat contacts are utilized, one of them being anelastic resistive member deformable against the other, the contact areaincreases only gradually with pressure. Furthermore, as the elasticmember is deformed against the other member, the spreading elasticmaterial tends to stickand suddenly slip, so that the contact area mayincrease in increments and thereby create noise.

Another source of noise in keyboard switches arises from the pick-up ofstray electrical signals. Such pickup can be minimized by positioning agrounded conductive plate near the switch to shield it from straysignals. However, if the moveable switch member mechanically vibratesrelative to the grounded plate, and if they are at a differentpotential, then the variable capacitance creates microphonicnoises'which may be heard in the organ output.

SUMMARY OF THE INVENTION In accordance with one embodiment of thepresent invention, an organ keyboard is provided for connecting signalsources to an amplifier in a manner that minimizes noise. The keyboardincludes an insulator board that supports a row of cylindrical wires,and a strip of insulative spacer material extending over the row ofwires and having windows leading to the wires. An elastic sandwich ofstrips extends above the spacer strip and can be deflected through thewindows in the spacer strip to contact the cylindrical wires. Thesandwich includes lower and upper strips of elastic conductive materialseparated by a middle strip of elastic insulative material. When adownward force is applied to the upper strip, a portion of the sandwichdeflects so that the lower strip passes through a window in the spacerstrip and into contact with one of the wires. Such downward forces areproduced when a musician depresses a key of the keyboard toprogressively flatten a leaf spring into the upper strip. The leafspring progressively lays the lower strip onto the cylindrical wire.This results in a progressively greater contact area between the lowerstrip and the cylindrical wire.

Each of the wires is connected to a different signal source while thelower conductive strip of the sandwich is connected to the input of thehigh gain amplifier. The progressive laying down of the lower conductivestrip on a wire produces a gradual decrease in contact resistance tominimize noise. The curvature of the round wire results in contact withthe strip being reliably established over a small area of the wire, sothere is a minimum of making and breaking of microscopic contact pointsas downward pressure on the strip increases. Both the lower elasticstrip and the wire are coated with a conductive lubricant, so thatspreading of the elastic strip onto the round wire occurs smoothlyrather than in a rapid stick-and-slip manner that would create noise.Each of the signal sources has a grounded terminal and the upperconductive strip of the sandwich is also grounded. The upper sandwichstrip shields the lower strip from stray currents. The fact that theupper and lower strips are fixed to an insulative strip between themmeans that they cannot vibrate relative to one another, and thereforenoises that could be created by such relative movements do not arise.

The novel features of the invention are set forth with particularity inthe appended claims. The invention will be best understood from thefollowing description when read in conjunction with the accompanyingdrawmgs.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a partial sectional end viewand partial schematic view of an organ constructed in accordance withthe invention;

FIG. 2 is a partial perspective view of the keyboard apparatus of theorgan in FIG. 1;

FIG. 3 is a partial sectional view of the keyboard of FIG. 1;

FIG. 4 is an enlarged view of a portion of the apparatus of FIG. 3;

FIG. 5 is a partial enlarged view taken on the line 5-5 of FIG. 4,showing the wire and lower strip thereof;

FIG. 6 is a partial perspective view of the apparatus of FIG. 5;

FIG. 7 is a plan view of the apparatus of FIG. 6;

FIGS. 8 and 9 are greatly enlarged views of the wire and lower strip. ofFIG. 5, illustrating the manner in which contact is made; and

FIG. 10 is a partial perspective view of an organ chord sectionconstructed in accordance with the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 illustrates an organwhich includes a plurality of signal sources l0, 12 which can beconnected through switch portions 14, 16 of a keyboard assembly to anamplifier 18 whose output drives a loudspeaker 20. The signal sources10, 12 generate a very low level tone or other signal which is highlyamplified by the amplifier 18, so that any noise generated at the switchportions l4, 16 will be highly amplified. The switch arrangement isconstructed to minimize the generation of noise as each switch portionis closed and also to minimize the pick-up of stray electrical current.

The switch arrangement includes a row of cylindrical electrical rods orwires such as wires 22, 24 that are connected to the tone generators l0,12. A contact strip 26 of highly elastic and particularly electricallyconductive material is positioned above the row of wires 22, 24, and isconnected by a conductor 28 to the input of the amplifier 18. When thecontact strip 26 is downwardly deflected into contact with one of thewires, as shown for the wire 22, signals from the tone generator canpass from the wire 22 to the contact strip 26 and to the amplifier 18for amplification and feeding to the loudspeaker 20. The row of wires22, 24 is supported on a support board 28' of insulative material. Thecontact strip 26 is normally spaced from the wires by a spacer strip 30which has windows 32 through which portions of the contact strip 26 canbe deflected. Deflection of the contact strip is accomplished when amusician depresses a key 34 with his finger.

The contact strip 26 is part of a sandwich 36 which includes a shieldingstrip 38 constructed of elastic and electrically conductive material,and which also includes a central strip 40 constructed of elasticinsulative material. The insulator strip 40 is fixed facewise to the twoconductive strips 26, 38, so that all portions of the sandwich deflecttogether. The shielding strip 38 is connected by a grounding wire 42 toground potential, and serves to isolate the contact strip 26 from strayelectrical currents.

As shown in FIGS. 3 and 4, each key 34 is pivotally mounted on a pivotbar 43 that lies on the support board 28'. A leaf spring 45 has arearward end portion fixed to the key 34 and an opposite forward endportion biased downwardly against the shielding strip 38. The shieldingstrip is mounted on a locater strip 49, and the forward end portion ofthe spring normally bears against the region of the shielding strip thatlies over the locater strip. As a musician depresses the forward portion34F of the key, the spring progressively flattens against the shieldingstrip, causing it to progressively lay down the contact strip 26 ontothe wire 22. Thus, after a large downward key movement, the spring mayhave the configuration indicated at 45A whkle the contract strip may bemoved down to the position 26A against the wire 22.

When the contact strip 26 is deflected and first begins to contact thewire 22, there is only a small area of contact between the strip ofwire. The strip 26 is constructed of a material of moderate resistance,or in other words only partial conductivity, so that a small area ofcontact results in a high contact resistance. As the strip 26 continuesto be downwardly deflected, it deforms over the wire so that a largerarea of the contact strip touches the wire to provide a relatively lowresistance contact. The high initial contact resistance eliminates muchof the popping sound that can occur when a low resistance contact issuddenly established between elements that may be at differentpotentials. The fact that the contact area rapidly increases with even asmall additional deformation of the contact strip 26, means that a lowresistance contact is quickly established that permits most of thesignal from the signal source to flow to the amplifier. When a musicianquickly depresses a key 34 with enough pressure to deflect the contactstrip 26 far enough to touch a wire 22, be generally has applied enoughforce to assure the quick establishment of low resistance through theswitch.

FIG. 6 illustrates the situation as the contact strip is rolled orprogressively layed down onto the wire 22. The initial contact point isat 5] while additional contact points rearwardly of italong the lengthof the wire are added, such as the point 53. All of these points liesubstantially at the top of the wire along the imaginary 7 the wire 22,due to the contact strip being progressively laid down, as well as alongthe width of the wire due to the contact strip being deformed slightlyby the higher pressure near the original contact point 51. There is onlya moderate increase in pressure around the original contact point 51, sothat the rubber-like material of the contact strip is not mashed whichwould greatly shorten its useful life.

It has been found that lower noise is produced by utilizing a wire 22 orother contact member which has a rounded upper surface, than one whichhas a flat upper surface. It is believed that this is due to a reductionin the making and breaking of microscopic contact points. FIGS. 8 and 9illustrate the condition which is believed to exist near the initialcontact point 51. The lower surface of the contact strip 26 is wavyrather than straight, and it changes shape as the pressure on itchanges. FIG. 9 shows the strip 26 when contact is first establishedbetween it and the wire 22, at the point 51. If the wire 22 had a flatupper surface, then the initial contact point might instead be atanother point 61 which is below the level of point 51 (indicated by theimaginary horizontal line 59 which passes through point 51). FIG. 9shows the strip 26 after additional downward pressure is applied to thestrip, which can cause local skewing and deformation of the strip. Ifthe wire 22 had a flat upper surface, then such skewing and deformationof the strip cause point 61 to lift off the flat surface and causecontact to be established at another lower point 63. Such breaking andmaking of contact results in noise.

In the case of the rounded wire 22, additional pressure merely increasesthe contact area around the initial contact point 51, because slightchanges in the orientation and shape of the contact strip 26 are notenough to lower the points 61 and 63 into contact with the wire. Once asubstantial area of contact is established around the point 51, thecontact resistance is low enough that any microscopic contacting andbreaking of contact has no noticeable effect. Thus, it is believed thatthe rounded wire 22 provides lower noise because it assures spreading ofcontact area around the initial contact point. Of course, it isnecessary that the strip 26 does not slide relative to the wire 22 afterinitial contact is established. This is assured by the mounting of thestrip 26 on the elastic shielding strip 38. Regardless of the way inwhich this is accomplsihed, however,

the rounded wire has been found to lower the noise as contact begins. Itshould be noted that the wire 22 has an elongated contact portion (whereit engages the strip 26) which is convex in only one plane, that beingthe plane which is perpendicular to its length.

As described above, the contact strip spreads largely sidewardly ontothe wire 22, as pressure increases at the locations where it has alreadytouched the wire. The elastic material of the contact strip 26 may havea relatively high coefficient of friction, so that there may be atendency for the material to repeatedly stick and slip as it spreads outalong-the wire. Such rapid sticking and slipping, which may be referredto as stician, can create noticeable noise. To minimize the creation ofsuch noise, a conductive lubricant indicated at 48 and 50 in FIG. 5 iscoated on the wire 22 and on the lower surface of the contact strip 26.The contact strip 26 may be constructed of a variety of materials suchas silicone rubber impregnated with carbon particles, and the lubricant48, 50 may be an extremely fine powered graphite.

The shielding effect provided by the grounded shielding strip 38 couldbe provided by a simple plate of conductive material rigidly mountedonthe organ near the contact strip 26. However, if the contact strip 26were to vibrate, then a signal would be generated due to such vibrationsand it would be fed to the amplifier 18. Such a signal would arisebecause the contact strip 26 normally has a voltage above groundpotential, in those cases where the signal sources l0, l2 generate toneswith D C components. A signal source which includes a photo-cell thatsenses light passing through an optical track is one example of such asource. In such an organ, the contact strip 26 quickly attains theaverage D C potential created by the signal source and is maintained atthat potential by a coupling capacitor 51. In the present keyboardarrangement, extraneous sounds are not created by vibrations of thecontact strip 26 relative to the shielding strip 38, because these twostrips are fastened together and cannot move relative to each other. Theinsulator strip is fixed facewise to both of the strips 26, 38 toprevent any relative movement of them apartand together. The insulatorstrip 40 may be constructed of rubberized electrical tape commonly usedin wrapping wires, but with adhesive on both faces. The shielding strip38 may be constructed in the same manner as the contact strip 26, as ofsilicone rubber impregnated with carbon particles. The spacer strip 30,which has the windows 32 through which portions of the contact strip 26can pass, can be formed of fish paper insulation or a variety of othermaterials. The use of numerous windows in a single strip facilitatesconstruction of the switch assembly. The sandwich 36 can be maintainedin a taut condition in extension over the spacer strip 30.

A main purpose of the shielding strip 38 is to intercept electromagneticwaves from the environment that might otherwise be picked up by thecontact strip 26 and be fed to the amplifier. A consequence (which maybe unwanted) of the closeness of the strips 26, 38 is that a highcapacitance existsbetween them. Any variation in the separation of thestrips 26, 38' would result in a variation in capacitance, and if thestrips 26, 38 are initially at a different DC potential then the changein capacitance tends to cause a change in voltage. This would cause acurrent flow from the contact strip 26 to the amplifier. If the strip 26vibrates, but the shielding strip 38 is stationary, then a rapid changein voltage on the strip 26 can occur, which results in a signal beingfed to the amplifier 18. This phenomenon is often referred to asmicrophonics. The present switch construction avoids microphonics bypreventing relative movement of the strips 26, 38, while stillpermitting deformation of the strip 26. The strip 26 may vibrate, but itis everywhere spaced from the shielding strip 38 by a constant distanceequal to the thickness of the insulating central strip 40.

The switch construction can be utilized in a variety of keyingarrangements. FIG. 10 illustrates a portion of a switch arrangement withbutton type keys 70, that is suitable for the chord portion of an organ.Each key or button is slideably mounted in a pair of plates 72, 74 andbears against a tab 76 formed in a plate 78 of spring material. Agrounding strip 80 carries a narrow insulator strip 82 and a narrowcontact strip 84. Regions of the contact strip 84 can pass down throughwindows 86 in a spacer strip 88 to contact cylindrical conductors 90.The conductors 90 are mounted on a circuit board 92 that has conductiveribbons which connect the wires to signal sources.

Thus, the invention provides a switch arrangement which is economical toproduce, and which minimizes the creation of noise in an organ that hassignal sources of low output. Contact noise is minimized by utilizingwires 22, 24 of stiff material such as brass, and with a convex surfacefor receiving a deformable contact strip 26. The contact strip 26 isconstructed of highly elastic material which is much more easilydeformed than the material of the wires 22, 24, and the area of contactof the strip 26 with the wires increases in a stable manner thatminimizes noise when it is progressively pressed against them. The useof a conductive lubricant on the wires and contact strip minimizesstician as the material of the contact strip spreads out on the wire,thereby minimizing this source of noise. The contact strip is shieldedfrom stray currents by a shielding strip 38 that is also constructed ofelastic material, and which is fastened to an insulator that is fastenedto the contact strip. The shielding and contact strips therefore cannotvibrate relative to one another, so that microphonic noise is minimized.Of course the insulating strip and shielding strips can be formed asfilms instead of relatively thick sheets.

Although particular embodiments of the invention have been described andillustrated herein, it is recognized that modifications and variationsmay readily occur to those skilled in the art and, consequently, it isintended that the claims be interpreted to cover such modifications andequivalents.

What is claimed is:

1. In an electronic musical instrument which includes a manuallyoperable switch for connecting an amplifier input to a signal sourcethat has first and second terminals, and in which the switch includes afirst sheet-like switch member that is easily deformable into contactwith another switch element, and in which the first sheet-like switchmember is connected to the amplifier while the switch element isconnected to the second terminal of the signal source, the improvementcomprising:

a second sheet-like member of easily deformable insulative materialfixed facewise to said first sheetlike switch member and a thirdsheet-like shielding member of easily deformable electrically conductivematerial fixed facewise to said second sheetlike member on a facethereof opposite said sheetlike switch member; and

means coupled to said third sheet-like shielding member and to saidfirst signal source terminal for preventing rapid changes in theirpotential with respect to each other, whereby to prevent vibration ofthe first switch member with respect to its shield.

2. The improvement described in claim 1 wherein:

said musical instrument includes a plurality of additional switchelements arranged in a row; and

said first sheet-like switch member and said second and third sheet-likemembers are of elastomeric material and are held in a taut condition inextension along said row of switch elements.

3. The improvement described in claim 1 wherein:

said means for preventing rapid changes in potential connects saidshielding member and said first source terminal together to maintainthem at the same potential.

4. An electronic musical instruement switch comprising:

a support;

an electrically conductive member mounted on said support, said memberhaving a convex contact portion facing away from said support;

a contact strip of electrically conductive and easily stretched anddeformed elastic material;

means for supporting said contact strip in a taut condition so itisspaced from said convex contact portion but can be deflected against it;

manually operable means for deforming said contact strip against saidconvex contact portion;

a strip of elastic insulative material fixed facewise to a face of saidcontact strip which lies opposite the face thereof which is nearest saidconductive membet;

a second strip of elastic electrically conductive material fixedfacewise to a face of said strip of insulative material which isopposite said first named strip of conductive material;

a signal generator having a grounded first terminal and having a secondterminal coupled to said conductive member;

an amplifier;

means for coupling the input of said amplifier to said first named stripof conductive material, and

means for grounding said second strip of conductive material.

5. An electronic musical instrument switch comprising:

a support;

an electrically conductive contact member mounted on said support;

a sandwich which includes a first strip of elastic conductive material,a second strip of elastic insulative material disposed facewise againstsaid first strip, and a third strip of elastic conductive materialdisposed facewise against said second strip on a face thereof which isopposite said first strip, the opposite faces of said second striprespectively fixed to said first and third strips to maintain said firstand third strips at a constant distance;

means for supporting said sandwich so that said first strip thereof isspaced from said contact member but can deflect against it;

manually operable key means for selectively pressing against said thirdstrip to cause said first strip to deflect against said contact member;

a signal source having first and second terminals;

means for coupling said second terminal of said signal source to saidcontact member;

an amplifier;

means for coupling the input of said amplifier to said first strip ofsaid sandwich; and

means electrically coupled to said first terminal of said signalgenerator and said third strip of said sandwich for maintaining saidfirst terminal at a constant potential with respect to said third strip.

1. In an electronic musical instrument which includes a manuallyoperable switch for connecting an amplifier input to a signal sourcethat has first and second terminals, and in which the switch includes afirst sheet-like switch member that is easily deformable into contactwith another switch element, and in which the first sheet-like switchmember is connected to the amplifier while the switch element isconnected to the second terminal of the signal source, the improvementcomprising: a second sheet-like member of easily deformable insulativematerial fixed facewise to said first sheet-like switch member and athird sheet-like shielding member of easily deformable electricallyconductive material fixed facewise to said second sheet-like member on aface thereof opposite said sheet-like switch member; and means coupledto said third sheet-like shielding member and to said first signalsource terminal for preventing rapid changes in their potential withrespect to each other, whereby to prevent vibration of the first switchmember with respect to its shield.
 2. The improvement described in claim1 wherein: said musical instrument includes a plurality of additionalswitch elements arranged in a row; and said first sheet-like switchmember and said second and third sheet-like members are of elastomericmaterial and are held in a taut condition in extension along said row ofswitch elements.
 3. The improvement described in claim 1 wherein: saidmeans for preventing rapid changes in potential connects said shieldingmember and said first source terminal together to maintain them at thesame potential.
 4. An electronic musical instruement switch comprising:a support; an electrically conductive member mounted on said support,said member having a convex contact portion facing away from saidsupport; a contact strip of electrically conductive and easily stretchedand deformed elastic material; means for supporting said contact stripin a taut condition so it is spaced from said convex contact portion butcan be deflected against it; manually operable means for deforming saidcontact strip against said convex contact portion; a strip of elasticinsulative material fixed facewise to a face of said contact strip whichlies opposite the face thereof which is nearest said conductive member;a second strip of elastic electrically conductive material fixedfacewise to a face of said strip of insulative material which isopposite said first named strip of conductive material; a signalgenerator having a grounded first terminal and having a second terminalcoupled to said conductive member; an amplifier; means for coupling theinput of said amPlifier to said first named strip of conductivematerial, and means for grounding said second strip of conductivematerial.
 5. An electronic musical instrument switch comprising: asupport; an electrically conductive contact member mounted on saidsupport; a sandwich which includes a first strip of elastic conductivematerial, a second strip of elastic insulative material disposedfacewise against said first strip, and a third strip of elasticconductive material disposed facewise against said second strip on aface thereof which is opposite said first strip, the opposite faces ofsaid second strip respectively fixed to said first and third strips tomaintain said first and third strips at a constant distance; means forsupporting said sandwich so that said first strip thereof is spaced fromsaid contact member but can deflect against it; manually operable keymeans for selectively pressing against said third strip to cause saidfirst strip to deflect against said contact member; a signal sourcehaving first and second terminals; means for coupling said secondterminal of said signal source to said contact member; an amplifier;means for coupling the input of said amplifier to said first strip ofsaid sandwich; and means electrically coupled to said first terminal ofsaid signal generator and said third strip of said sandwich formaintaining said first terminal at a constant potential with respect tosaid third strip.